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201.
The pulsed positron beam at the Helsinki University of Technology is designed for the end energy of 3-30 keV and grounded target. This is achieved with a constant voltage acceleration followed by an adjustable deceleration. In the design of this accelerator-decelerator the possibility for electrical breakdowns and partial discharges must be eliminated.For designing the electrode and insulator structures for accelerator-decelerator configuration electric field simulations were carried out with the finite element analysis program. In this paper we present the design of the accelerator-decelerator and the results of the electric field simulations. The results of high voltage tests will also be presented and compared with the simulations. 相似文献
202.
203.
204.
Mass transport due to electromigration can be estimated if the diffusion coefficientD and the electromigration effective charge numberZ* are known. Neutron activated tracer scanning method determine the radioactivity at different positions. An automatic scanning
system for determining the radioactive concentration profiles developed using a microprocessor is described in this paper.
Using the radioactive concentration profiles the electromigration shift is determined. From this shift the electromigration
effective charge numberZ* is calculated. The system developed was tested for tin thin films. 相似文献
205.
D. K. Kuznetsov I. S. Baturin V. Ya. Shur N. Menou C. Muller T. Schneller A. Sternberg 《Physics of the Solid State》2006,48(6):1174-1176
The effect of irradiation with electrons and neutrons and of exposure to synchrotron radiation on cyclic switching of polarization in thin films of lead zirconate titanate Pb(Zr,Ti)O3 (PZT) was studied. It is shown that variations in the shape of switching currents are due to the generation of a spatially nonuniform bound internal field with account for an increase in the rate of bulk screening caused by irradiation. A correlation between structural variations and the evolution of the switching current measured during and after irradiation is established. 相似文献
206.
Current techniques of water wave visualization such as shadowgraphy and stereo photography are widely used but are deficient
in many aspects. Refraction based visualization observes the bending of light as it traverses across a liquid-air interface.
This work describes the continued development of techniques to measure the surface height of a liquid free surface. The method,
Reference Image Topography, utilizes refraction of light at the free surface as a function of the local angle of that surface.
Particle Image Velocimetry (PIV) software is used to evaluate apparent dislocations of the target image viewed through the
free surface, which are approximately proportional to the surface angle. High-resolution images are presented of the dynamic
surface topography for a point source and the shallow water flow around a vertical cylinder. 相似文献
207.
208.
We examine the optical near-field interaction between different types of scanning tips and single oriented fluorescent molecules.
We demonstrate the influence of a tip on the excitation intensity as well as on the integrated fluorescence signal, the excited
state lifetime, and the angular emission of single molecules. By using a standard model describing the radiation of an oscillating
dipole close to a nanosphere or a flat interface, we interpret our observations and describe some central criteria for obtaining
fluorescence enhancement or quenching.
PACS 33.80.-b; 07.79.Fc; 78.90.+t 相似文献
209.
von Eynatten G. Ritter T. Bömmel H. E. Dransfeld K. 《Zeitschrift für Physik B Condensed Matter》1987,65(3):341-345
A new model is presented which explains well the dramatic decrease of the Mössbauer line intensities with raising temperatures for freely dispersed iron microscrystals. In contrast to other theories which consider mainly vibration to be responsible we discuss here the decrease in terms of large amplitude diffusive rotational or translational jumps of the particles. Such diffusive jumps lead — in agreement with the observation — to a strong reduction of the Mössbauer-intensity without broadening the line width in a noticeable way. The typical potential well for a diffusing particle in an equilibrium position is derived quantitatively to be 13 meV. The model might be important also for a new understanding of the dynamics of catalytic clusters either in contact with each other or with larger solid surfaces.Part of this work was supported by the DFG Sonderforschungsbereich 306, Konstanz 相似文献
210.
In this paper, we study an evasion problem in systems described by equations of parabolic type. We consider four versions of constraints on the control parameters. 相似文献